chapter 7

Using concepts from Chapter 3, which statement best explains why proteins—and not RNA, DNA, carbohydrates, or lipids—are the molecules responsible for "reading" the array of molecular zip codes in cells?

Because proteins can have diverse structures and chemical properties, different proteins can "read" different zip codes by interacting specifically with them.

Choose the letter that indicates the organelle that contains most of a cell's DNA.

C The nucleus contains most of a cell's DNA.

What scientific hypotheses can be tested by a pulse-chase experiment?

Movement of molecules through a cell over time

Which answer most accurately summarizes the (1) structural and (2) functional properties of actin filaments, intermediate filaments, or microtubules?

intermediate filaments: (1) many subunit types; (2) one cellular role Correct. Although intermediate filaments can be built from a variety of subunit types (keratins, lamins, or others), they serve purely a structural role (see p. 129).

Which organelle plays a role in intracellular digestion?

lysosome The prefix "lyso-" means decomposition.

Which of these are hollow rods that shape and support the cell?

microtubules Microtubules are rods that also play a role in organelle movement.

The cilia and flagella of eukaryotic cells are composed of _____.

microtubules Eukaryotic cilia and flagella are composed of microtubules.

Which of the following is a correct match of cell type with structure?

muscle cell ... has proteins that slide back and forth These proteins help muscles to contract.

Where is a bacterial cell's DNA found?

nucleoid region Bacteria lack a nucleus; their DNA is found in the nucleoid region.

Ribosomal subunits are manufactured by the _____.

nucleolus Ribosomes are manufactured by the nucleolus.

Which of these organelles carries out cellular respiration?

mitochondrion Mitochondria convert the chemical energy of organic molecules to chemical energy in the form of ATP.

For prokaryotic cells, which statement is correct concerning how the structure of a particular cell component correlates with its function?

The cell wall is a tough, fibrous layer that protects the cell and gives it shape and rigidity.

During a pulse-chase experiment, photographic emulsions were prepared at different times during the chase, and radioactive spots were detected at the following times and locations: 5 minutes: rough ER; 10 minutes: Golgi apparatus; 40 minutes: endosomes; 70 minutes: lysosomes; 140 minutes: lysosomes. Which of the following conclusions can be drawn from these results?

The final destination of the proteins was the lysosome.

The _____ is composed of DNA and protein.

chromatin Chromatin is composed of DNA and protein.

In a bacterium, where are proteins synthesized?

ribosomes Ribosomes are involved in the manufacture of polypeptides (proteins).

Which of these manufactures cellular membranes by adding membrane proteins and phospholipids to its own membrane?

rough endoplasmic reticulum As membrane proteins grow from ribosomes on rough ER, the proteins are embedded into the rough ER membrane.

Where is calcium stored?

smooth endoplasmic reticulum In addition to storing calcium, the smooth ER also plays a role in detoxification and lipid synthesis.

Which of these structures stores, modifies, and packages products?

A The Golgi apparatus modifies, stores, and packages products of the ER.

Which of the following results provided evidence of a nuclear localization signal in the nucleoplasmin protein?

After cleavage of the protein, only the tail segments appeared in the nucleus.

_____ is/are identical in structure to centrioles.

Basal bodies Basal bodies and centrioles have identical structures.

The structure that regulates the passage of material into and out of this bacterial cell is indicated by the letter _____.

C The plasma membrane is selectively permeable.

Molecules move into and out of the nucleus through the _____.

Correct. The nuclear pore complex directs movement of molecules into and out of the nucleus.

The DNA-containing region of this bacterial cell is indicated by the letter _____.

D The nucleoid region contains DNA

Which of these provides the cell with structural support?

D Microfilaments are a component of the cytoskeleton.

Which of the following cell structures is only found in algal and plant cells?

D) chloroplasts Correct. Chloroplasts contain chlorophyll and are responsible for photosynthesis.

Which of these is the double membrane that encloses the nucleus?

E This is the nuclear envelope.

Pancreatic cells, which secrete a large amount of digestive enzymes, are labeled with radioactive leucine and then chased for several hours with nonradioactive leucine. Photographic emulsions are prepared at different times during the chase. Where would the black spots appear on an emulsion prepared 3 hours after the pulse?

Exterior of the cell Black spots would appear on the exterior of the cell after 3 hours, indicating that the proteins had been secreted from the cell.

_____ are surface appendages that allow a bacterium to stick to a surface.

Fimbriae Fimbriae enable bacterial cells to stick to a surface.

What is the first step in a pulse-chase experiment?

Incubating cells with a labeled molecule Cells are first "pulsed" with a large amount of labeled material for a short time.

_____ are the sites of protein synthesis.

Ribosomes Ribosomes are the site of protein synthesis.

What path does a protein in the secretory pathway take, starting from its site of synthesis?

Rough ER, Golgi apparatus, secretory vesicles, plasma membrane

Which statement most accurately describes what happens to proteins that lack an ER signal sequence?

They are released into the cytosol. Correct. Ribosomes synthesizing proteins without ER signal sequences remain in the cytosol and release the proteins there.

How are these signals read?

They bind to receptor proteins.

What three distinct elements make up the cytoskeleton in eukaryotic cells?

actin filaments, intermediate filaments, and microtubules Correct. Actin filaments are also known as microfilaments.

What name is given to the rigid structure, found outside the plasma membrane, that surrounds and supports the bacterial cell?

cell wall The cell wall is a rigid supporting structure.

True or false? Proteins produced during the "chase" phase of a pulse-chase experiment are labeled with radioactive material

false. During the chase phase, cells are provided with a large amount of nonradioactive material, so they are not labeled.

The _____ is a selective barrier, regulating the passage of material into and out of the cell.

plasma membrane The plasma membrane regulates the passage of material into and out of the cell.

The _____ is the bacterial structure that acts as a selective barrier, allowing nutrients to enter the cell and wastes to leave the cell.

plasma membrane The plasma membrane is selectively permeable.

What is the function of a bacterium's capsule?

protection A bacterium's capsule has a protective role.

Which of these organelles produces H2O2 as a by-product?

peroxisome Peroxisomes produce hydrogen peroxide as a by-product of their metabolic processes.